Ms Ardern said the buy-back could cost up to NZ$200m ($138m; £104m), but "that is the price that we must pay to ensure the safety of our communities".

Graham Eva

Our actions, on behalf of all New Zealanders, are directed at making sure this never happens again.

Jacinda ArdernPrime Minister of New Zealand

The prime minister has called the Christchurch attacker a terrorist and said she will not utter his name.

The gunman, armed with semi-automatic rifles including an AR-15, is believed to have modified his weapons with high-capacity magazines - the part of the gun which stores ammunition - so they could hold more bullets.

Analysis: An overwhelming drive for change

By Phil Mercer in Christchurch

Image copyrightAFP

New Zealand has tried - and failed - to reform its gun laws several times in the past two decades, but the momentum for change is now overwhelming. Owners will be forced to surrender proscribed firearms and will be compensated, but those who resist could be prosecuted.

A major hurdle for the authorities is that no-one knows how many assault rifles and military-style semi-automatic weapons are out there. New Zealand's Police Association has said there also needs to be a register of all guns and their owners.

That could happen in the next round of amendments promised by the prime minister, which will focus on licensing and registration. She has broad public support following the atrocities in Christchurch.

Earlier, MPs in the capital, Wellington, were handed a petition with more than 65,000 signatures demanding tougher laws. Some gun owners aren't happy, insisting that vetting procedures were already strict enough. They are, though, swimming against the tide.

What has the reaction been?

Survivor Kawthar Abulaban, 54, who was at the Al-Noor mosque, welcomed the move: "It's a good thing, why would we need to have guns like this in our houses?" she told AFP.

The leader of New Zealand's opposition National Party, Simon Bridges, backed the changes and said it was "imperative in the national interest [that] we keep New Zealanders safe."

The move drew strong responses in the US, where campaigners against gun violence frequently clash with the pro-gun lobby.